Power element having novel forcetransmitting plug



Oct. 23, 1962 s. VERNET ETAL 3,059,475

POWER ELEMENT HAVING NOVEL FORCE-TRANSMITTING PLUG Filed May 9, 1956 INVEN TOPS 5 5 VERNET By G: ASA/(4M4 5mm 0mm, [av/s t M645 4 TTORNEVS Thisinvention relates to a power element operable by pressure change in apressure-producing material. The pressure-producing material may be acontained thermally expansible material as for example disclosed inUnited States Patent No. 2,259,846, or the pressure-producing materialmay be a pressure fluid introduced from a remote source as illustratedin FIG. 3 of United States Patent No. 2,534,497.

Power elements of the above discussed type usually include a housing forthe pressure-producing material, and a piston slidably mounted in thehousing. Pressure change in the pressure-producing material causes thepiston to move rectilinearly into and out of the housing. Necessarymultiplication of the linear piston movement relative to that of thepressure-producing material is effected by providing a body or plug offorce-transmitting material in a tapering chamber between thepressure-producing material and piston.

Objects of the present invention are to provide a power element of theabove-mentioned type wherein:

1) The plug of force-transmitting material is a low friction,non-sticking, pliable material having the ability to easily reshapeitself in accordance with such changes in the contour of its housing asoccur during movement of the power element piston; thereby offeringminimum resistance to piston movement and permitting formation of thepower element as a comparatively small, low cost device,

(2) The plug reshaping characteristic is obtained without any suchliquidity or fluidity a would cause the plug material to extrude or flowinto the clearance spacebetween the piston and its housing; therebyenabling the power element to retain its calibration over a large numberof cycles,

(3) The plug retains its reshaping and lack of fiuidity characteristicsover a wide range of temperatures, as for example between minus 80 F.and 500 F.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

In the drawing FIG. 1 is a sectional view of a power element constructedaccording to the present invention.

Before explaining the present invention in detail, it is to beunderstood that the invention is not limited in its application to thedetails of construction and arrangement of parts illustrated in theaccompanying drawings, since the invention is capable of otherembodiments and of being practiced or carried out in various ways. Also,it is to be understood that the phraseology or terminology employedherein is for the purpose of description and not of limitation.

In the drawing there is shown a power element 1 including a housing 2, abody or pellet of wax or other thermally-expansible, pressure-producingmaterial 3, a movable wall or piston 4, a corrugated stainless steeldiaphragm 5, and a body of pliable force-transmitting material 6. A disc7 of polytetrafluoroethylene is positioned between material 6 and piston4 in order to prevent material 6 from extruding into the clearance space9 between piston 4 and its bore 8. A spring (not shown) is pro-3,059,475 Patented Oct. 23', 1962 vided for returning piston 4 to itsillustrated position during pressure decrease in material 3.

Force-transmitting material 6 consists of discrete resinous particlesdispersed in a flowa'ble polysiloxane. Preferably the discrete resinousparticles are formed of poly tetrafluoroethylene,polymonochlorottifluoroethylene or nylon. The polysiloxane preferablyincludes a major pro portion of dimethyl polysiloxane and a minorproportion of diphenyl polysiloxane. The discrete resinous particlespreferably comprise between and by volume of the force-transmittingmaterial with the remainder being the polysiloxane. Some pliabilityadvantages may be obtained by operating with volume percentages ofresinous particles above 90% but the polysiloxane tends I to flow intoclearance space 9 when the volume percentage of the resinous particlesis below 75%.

The molecular weight of the flowable polysiloxane is preferably such asto obtain polysiloxane viscosities above 1000 centistokes at 25 C.Preferably the polysiloxane viscosity is about 2,000,000 centistokes at25 C. Below polysiloxane viscosities of 1000 centistokes thepolysiloxane is so fluid as to leak into clearance space 9. Polysiloxanehaving a viscosity of 2,000,000 centistokes is very slowly flowa'ble,i.e. if a lump of it were placed on a table it would require severalhours to lose its lump shape.

Preferably force-transmitting material 6 is compounded the resinousparticles with the polysiloxane and solvent,

and thereafter drive oh the solvent at a temperature between 300 F. and400 F. The resulting mixture of discrete resinous particles and fiowablepolysiloxane is admirably suited for use as a pliable force-transmittingmaterial in the FIG. 1 power element.

In operation of the FIG. 1 power element atemperature increase inambient atmosphere 10 causes material 3 to expand so as to exert anupward pressure against corrugated diaphragm 5. Diaphragm 5 thereby isflexed upwardly so as to push material 6 upwardly into cylindrical bore8 and move piston 4 in the arrow 11 direction against the action of itsreturn spring (not shown).

It will be noted that piston 4 is quite small in diameter, and conicalsurface 12 (which confines material 6) converges quite rapidly, i.e. theangle 13 which it makes with diaphragm 5 is fairly small. Also aconsiderable diaphragm area is exposed to material 6. These factors,coupled with the pliable character of material 6 enable pellet 3 to beformed large enough to produce a considerable movement of material 6into bore 8 and a correspondingly long linear movement of piston 4 inthe arrow 11 direction. Because of the considerable movement offorce-transmitting material 6 into bore 8 material 6 undergoes aconsiderable amount of reshaping. In the past there have been employedas force-transmitting materials various types of deformable materialssuch as Ameripol, andneoprene. These deformable materials were howevernot flowable and could not undergo the deformation taking place in theFIG. 1 construction without exerting considerable pressures against thewalls of housing 2. Such pressures (particularly those exerted againstthe wall formed by bore 8) offered considerable resistance to returnmovement of piston 4 and therefore necessitated the use of fairly heavyreturn springs if piston 4 was to keep pace time wise with the conditionof atmosphere 10 during temperature decrease. Such heavy return springsexert considerable forces against the power clement walls, and the powerelement walls must therefore be relatively thick in order to withstandthe forces. The power element housings are usually constructed of highcost brass, and it is therefore economically desirable to limit theamount of housing material; however, as indicated above, this hasheretofore not been possible. An

the present invention includes discrete resinous particles dispersed ina ilowable polysiloxane. The discrete character of the resinousparticles, coupled with the coating of polysiloxane around eachparticle, enables the individual resinous particles to easily changeposition with respect to one another without sintering into a solidimmovable mass at the high temperatures (sometimes above 400 F.) towhich the power element may be subjected.

The polysiloxane employed in the present invention has a comparativelyflat viscosity curve when plotted against temperature; i.e. theviscosity at 150 F. is almost the same as at 400 F. Also thepolysiloX-ane does not tend to decompose at the higher temperatures. Asa result the polysiloxane does not tend to flow into clearance space 9at the higher temperatures or solidify at the lower temperatures.Because of this characteristic of the polysiloxane the power element can.be employed in ambient atmospheres undergoing large temperaturechanges, as for examplein aircraft applications.

The pliable or reshaping characteristics of material 6 are not obtainedat the expense of increased fluidity or tendency to flow into clearancespace 9. 'Thus, by

utilizing 'a material containing only 25% by volume of" flowablepolysiloxane and employing a polysiloxane haw ing a viscosity above 1000centistokes it is possible toprevcnt leakage of material 6 intoclearance space 9 and still retain the desired pliability. When thepower element is to be used only in the higher temperature ranges (300F. to 400 F.) the volume percent of the polysilox'ane may beadvantageously reduced to approximately 10% or less since the pliabilitycharacteristic contributed by the polysiloxane is enhanced by slightlylowered viscosity characteristics. The discrete resinous particles(particularly when polytetrafluoroethylene is employed as the resinousmaterial) contribute lubricating and non-sticking characteristics tomaterial 6, and thereby enable the material to move into and out of bore8 without sticking or clinging to the housing interior surfaces.

We claim:

1. In a power element," the combination comprising a housing structuredefining a guideway and a flaring passageway extending therefrom; apiston reciprocably fitting said passageway; and a plug body of pliableforce-transmitting material within the flaring passageway in operativeengagement with the piston; said force-transmitting material comprisingdiscrete solid resinous particles dispersed in and coated by a fiowableorganic polysiloxane, said discrete particles occupying between 75% and90% of the plug body volume, the arrangement of the resinous particlesdispersed in the flowable polysiloxane serving to isolate the resinousparticles from one another so as to permit said particles to easilyshift relative to one other in response to pressure development on theplug body.

2. The combination of claim 1 wherein the polysiloxane includes a majorproportion of dirnethyl polysiloxane and I a minor proportion ofdiphenyl polysiloxane.

3. The combination of claim 1 wherein the viscosity of the polysiloxaneat 25 C. is above 1000 ccntistokes.

4. The combination of claim 1 wherein the discrete particles areselected from the group consisting of polytetrafluoroethylene,polymonochlorotiifluoroethylene, and nylon.

5. The combination of claim 1 wherein the discrete particles are formedof polytetrafluoroethylene.

6. The combination of claim 1 wherein the discrete particles are formedof polymonochlorotrifiuoroethylene.

7. The combination of claim 1 wherein the discrete particles are formedof nylon.

8. The combination of claim 1 wherein the fiowable polysiloxanecomprises about 20% of the plug material volume.

9. The combination of claim 1 wherein the viscosity of the polysiloxaneat 25 C. is between 1000 centistokes and 2,000,000 centistokes.

References Cited in the tile of this patent UNITED STATES PATENTSFOREIGN PATENTS 702,868 France Apr. 18, 1931

